Will air passengers take heed and buckle up?

The terrifying plunge of a United jumbo jet that took one life and injured 102 people is unlikely to result in stricter air safety regulations and will do little to jolt passengers out of their complacency about seat belts, aviation officials say.

"People have become so comfortable with air travel that they forget there's an incredibly hostile atmosphere outside their window," said Patricia Friend, international president of the Association of Flight Attendants, representing 40,000 attendants. "The sky looks calm, so people disregard seat belt signs and forget about turbulence."Turbulence is the leading cause of injuries to passengers, injuring an estimated 58 people every year aboard U.S. planes. Almost all passengers who've been severely hurt since 1981 were not wearing seat belts, according to the Federal Aviation Administration.

Passengers recounted a free-fall so violent that those standing in the aisles were thrown several feet into the air.

Konomi Kataura, 32, of Tokyo, died of internal bleeding in her head. More than 100 people were treated for injuries.

It is not known how many of those injured were wearing seat belts.

Although not all the passengers agree, United spokeswoman Mary Jo Holland said the fasten seat belt signs had been turned on right before the turbulence hit.

The flight data recorder, shipped to the U.S. National Transportation Safety Board Monday, will be used to investigate the cause of the accident. The flight crew and passengers will be interviewed to determine how many of those injured were wearing seat belts.

United's policy, like that of other major carriers, encourages passengers to buckle up regardless of whether the seat belt light is illuminated, Holland said.

"Crew members encourage passengers to wear their seat belts while seated," she said. "But once the sign is off, it's at the passengers' discretion. If they disregard warnings, that's their decision."

The FAA requires passengers to be seated with their seat belts fastened when a plane leaves the gate and after takeoff, during landing and until the aircraft stops, and whenever the seat belt sign is illuminated during flight.

Unless a pilot who has previously traveled along the same route warns another pilot of turbulence - referred to as "chop" - it is virtually undetectable, according to David A. Fuscus, spokesman for the Air Transport Association of America, which represents 22 carriers.

"Clear-air turbulence happens at high altitudes when a low pressure front and a high pressure front meet," Fuscus said. "The force of them meeting causes a movement of air that can be mild or, in rare cases, can create a vortex, a kind of tornado in the sky.

"This is a harsh reminder that the atmosphere is anything but calm. Passengers need to remember there's turbulence every day, over water, mountains, deserts. It doesn't matter whether you're above the Pacific Ocean or above Iowa."

Fuscus believes it's unlikely a law similar to one imposed on car passengers, mandating seat belt use at all times, would be approved for air travelers.

"Having said that, what those of us in the industry would like to see come out of this is recognition from passengers that they have a role in ensuring their own safety," Fuscus said. "They should not ignore safety briefings and advice from pilots."

Between 1981 and 1996, there were 252 reports of turbulence affecting major air carriers. Two passengers died, and 863 suffered minor injuries. Of the 63 passengers seriously injured, 61 were not wearing seat belts, the FAA says.

Two-thirds of all turbulence-related accidents occur at or above 30,000 feet.